Apparatus for the reproduction of music, speech and the like



June 1931. F. w. LANCHESTER 1,309,483

APPARATUS FOR THE RE RODUCTION OF MUSIC, SPEECH, AND THE LIKE Filed Sept. 8, 1930 Patented June 9, 1931 UNITED STATES" PATENT? OFFICE FREDERICK WILLIAM LANGHESTER, OF MOSELEY, ENGLAND APPARATUS FOR THE REPRODUCTIQN OF MUSIC, SPEECH AND THE LIKE Application filed September 8, 1930, Serial No. 480,484, and in Great Britain September 14, 1929.

The present invention relates to improvements in apparatus for the reproduction of music, speech and the like and refers more particularly to an improved electro-magnetic '5 device commonly known as a pick-up by means of which movements impressed upon a needle by a record are caused to give rise to voltage variations which are capable of subsequent'amplificationfor the electrical reproduction of sound through the medium of a socalle'd'lou-d speaker or electrically operated sound emission device. p

The objects of the present invention are to avoid excessive weight to be borne by the needle, more especially where such weight involves mass situated directly over the needle, to dispose the mass as nearly as possible in the line of the needle reaction in order to provide an inertia anchorage, and to simplify construction and cheapen production.

In electro-magnetic pick-ups as commonly constructed there is amagnetic circuit of the closed type only interrupted by the working air gaps. According to the present invention a permanent magnet is employed in the form of a bar conveniently constituting a connecting member between a pivot piece or block and a spool carrying the winding, needle, holder needle etc., the magnetic circuit being an open circuit the lines of force or field having no return path other than through the surrounding air or space.

In one mode of carrying the present invention into effect the head of the pick-up comprises a spool wound with some'few thousand turns of insulated wire of about 46 or 48 s. w. g, The top and bottom flanges of the spool are of suflicient thickness to permit of saw cuts or grooves being cut transversely '40 in their substance to form housings for the projectingprongs of a pole piece and a pole plate, these prongs extendingtowards one another but leaving gaps between their extremities, one gap being above the winding '45 and the other below. Thespool, pole piece and pole plate assemblage constituted as above described is carried by a bar magnet whose normal position is approximately horizontal, the said magnet being connected to the pole piece atone end and to apivot block forming the means of mounting at the other. The pivot block is conveniently a short rod of cylindrical form mounted to pivot upon centres. Referring to the accompanying sheet of illustrative drawings which illustrate various examples of carrying the invention into prac tice and in which like letters refer to like parts throughout i Figure 1 is an elevation of a pick-up. 7

Figure 2 a plan view; 8

Figure 3 is an end View showing the head and needle set to an appropriate angle in relation to the record. i

Figure4 shows components hereinbefore referred to as pole plates, and

Figure 5 represents one of these in end view.

Figure 6 represents the spool and winding in side and end view.

Figure 7 is illustrative of the manner in which the pickup may be appropriately mounted.

. Figures 8 and 9 show in elevation and plan respectively a modified construction.

Referring to the figures generally; 1 isa bar magnet mounted in the pivot block 2 by the grub screw 8; the magnet carries the pole piece 4 between the prongs of which is mounted the spool 6 carrying the winding 8, the said prongs being accommodated in the slots 7, 7 a pole plate (laminated) 5 is similarly mounted in the slots 7, 7 of the spool 6. The pole piece 4 may be integral with the bar magnet or it may be separately formed conveniently in two parts e. g. pressed from sheet. iron and riveted together. The ends of the winding 8 are brought out through the upper end of the spool and gripped by screws 10 under plates 9, the output leads being similarly connected. A flat at an appropriate angle is cut at 15 in order that the spoolshall not be liable to foul the record 14. v A

Referring now more particularly to Figure 7 the pivot block 2 is pivoted upon centre screws 18,13 on a swing arm 11 carried in turn on a vertical pivot 12. A record 14 (part only) is shown, the arrow indicating the customary direction of rotation. In Figures 8 and 9 a cast magnet of T form'is New shown, separate components 2 and a being dispensed with.

It will be understood that the magnetic circuit starting at the magnet proper passes by way of the pole piece 4 through the two gaps (Figure 4) in parallel into the pole plate 5 and thence through the surrounding air to the pivot block 2 and back to the magnet. The piece 4 and pole plate 5 are preferably laminated in the manner indicated in Figure 2 and the protruding portions of the latter are separated and spread out in order to allow the magnetic flux to pass into the air with minimum reluctance; as shown the laminae are three in number but a greater number may be used with advantage, they are shown held together by two rivets 5a, 5a. The pole plates 5 however are not essential but if omitted the signal is weaker. The angle of trail of the needle may be set as required by means of the grub screw 8, the fit of the magnet in the pivot block being such as to permit of rotary adjustment. In such case as when the pole piece 4 is made from the solid the rongs may be subdivided by slitting with a fine saw to obtain the advantage of lamination; this is less necessary if the piece be made of two sheet iron pressings since in this case the junction divides the pole prongs in the lane of the centre line in the end View. he pole prongs may be forged or otherwise formed as part of the magnet itself in whieh case the separate pole piece is not required as mentioned above. 7

The needle 16 is shown as itself constituting the armature and mounted in a rubber bush but this feature forms no part of the present application. The needle may be mounted in or attached to a separate armature and the said armature may be mounted in any suitable or known manner, suitable rovision being made. For example a small bracket may be mounted on the top of the spool 6 drilled in line with the spool axis to hold the butt end of the needle or reed, the ordinary clamp screw being used to secure same.

V In a pick-up constructed as hereinbefore described an adequate magnetic field may be secured by a cobalt steel magnet from about 8 to 10 m. m. diameter by or m. m. length of weight sa from one to two ounces, (but I do not con ne myself to those dimensions) and the weight of magnet steel borne by the needle is less than half of this. It is easy therefore to construct a pick-up in accordance with the present invention in which less than one ounce total weight is borne by the needle'and yet a magnet of adequate power is employed. This reduction of weight has many advantages; the wear of the record is diminished in far greater proportion than the mere reduction of needle load, moreover the same needle may be used many times Since the needle point wear is almost-negligible. Alternatively where the needle is used in itself as the armature a needle of soft lowhysteresis iron or alloy may be used, a hardened point being no longer necessary. The weight in question borne by the projected area of the needle point, the latter being ap proximately 20 millionths of a,square inch, gives a pressure per square inch on the needle point of 8000 pounds which may be said to lie within the range of good engineering practice and such as will permit of the needle point being floated on a film of lubricant whether the said lubricant be applied independently or whether the composition of the record be such as to be self-lubricating.

Furthermore, although it is possible to relieve the weight on the needle in a pick-up of the ordinary kind by counterpoise, this adds to insteadof subtracting from the inertia forces which arise when the record is warped or the table is not true, and a counterpoised pick-up is unsatisfactory for this reason. Owing to the fact that in a pick-up constructed in accordance with the present mventionthe centre of percussion of the assemblage about the pivot 13 is distant from the pivot less than the radius to the needle point, the latter is able to follow irregularitiesin the record without any disturbance being apparent in the rendering, to an extent not ordinarily possible.

Pick-ups constructed in accordance with the present invention are easy to manufacture and assemble. The final magnetization should take place after assembly. In the case of the example illustrated in Figures 1 and 2 the pivot piece 2 is placed. in contact with one of the poles of a powerful electro-magnet and the pole plate or plates 5 being placed in contact with the other pole, it is desirable to use special pole adapters to minimize the reluctance at the points of entry and exit of the magnetizing field. A needle or temporary armature may be placed in the pole gaps during magnetization but this is un-; necessary if the electro-magnet used be of suflicient power; it is desirable to employ an electro-magnet'of some 20,000 or more ampere turns. 0

Having now described my invention, what I claim as new and desire to secure by Letters Patent is 1. A pick-up to be used in conjunction with a record for the reproduction of music, speech, and the like'in which a permanent magnet constitutes at least part of the supporting arm radially arranged in relation to the pivotal mounting of the pick-up.

2. A pickup in accordance with claim 1 in which the magnetic circuit isan open circuit that is .to say in which the magnetic flux (or lines of force) sustained by and passing through the magnet find their return path by wa of the surrounding air.

.3 A pickup in accordance with claim 1 including a winding surrounding a needle or armature, a grooved spool carryin said needle or armature, a pole piece attac ed to the magnet having projections engaging said grooves and a plate having projections also engaging said grooves. c

4. A pick-up as claimed in claim 1 wherein said magnet is of T form, one limb of which being pivoted and the other limb embodying a separately formed pole piece and carrying a winding.

5. A pick-up as claimed in claim 1 wherein said magnet is of T form, one limb of which being pivoted and the other limb embodying an integral bifurcated. pole piece carrying a winding.

6. A pick-up as claimed in claim 1 wherein the total weight borne by the needle does not exceed about one ounce.

In testimony whereof I have signed my.

name to this specification. r

FREDERICK WILLIAM LANCHESTER. 

